An improvised explosive device equivalent of around 4 kg TNT has been found in the main hydraulic unit at Irganaisk hydroelectric power plant in Russia's North Caucasus republic of Dagestan, where a fire broke out on Wednesday evening, a source in the regional authorities said.

"The strength of the improvised explosive device, which was made from ammonium nitrate, was around 4 kg TNT. It was equipped with an electric detonator. It looks like the bomb was to be detonated remotely," the source said.

He said the explosive device was discovered on Wednesday night when the plant was being searched after the fire.

A local police source earlier said that the detected explosives and the fire were not connected.

"Specialists have confirmed that the fire occurred for technical reasons and was not the result of a terrorist attack," the source said.

Federal Security Service officials have deactivated the bomb.

The Irganaisk plant is the largest derivational hydroelectric plant in Russia, with two radial-axial hydraulic units with a capacity of 200 megawatts.

Sporadic terrorist attacks and militant clashes are common in Russia's largely Muslim North Caucasus republics, especially Dagestan, Chechnya and Ingushetia.

In July a group of gunmen set off five bombs with up to 3 kg of TNT at the Baksan Hydropower Plant in the North Caucasus republic of Kabardino-Balkaria, killing two police officers. The blaze from the blast covered an area of 250 square meters.

MOSCOW, September 9 (RIA Novosti)